| Issue |
93152
|
| Summary |
LLVM ERROR: Broken function found after pass "LowerSwitchPass", compilation aborted!
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
mikaelholmen
|
llvm commit: 4cc6d0f4dfb26d
Reproduce with:
```opt -passes="lower-switch" -verify-each bbi-95731.ll -o /dev/null```
Result:
```
PHINode should have one entry for each predecessor of its parent basic block!
%tmp = phi i3 [ 0, %LeafBlock ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ]
LLVM ERROR: Broken function found after pass "LowerSwitchPass", compilation aborted!
```
If we look at what lower-switch actually produces (-print-after-all) we see
```
; *** IR Dump After LowerSwitchPass on v_257_0 ***
define void @v_257_0(i3 %0) {
bb.0:
br label %LeafBlock
LeafBlock: ; preds = %bb.0
%.off = add i3 %0, 2
%SwitchLeaf = icmp ule i3 %.off, -4
br i1 %SwitchLeaf, label %bb.1, label %bb.2
bb.1: ; preds = %LeafBlock
%tmp = phi i3 [ 0, %LeafBlock ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ]
br label %bb.2
bb.2: ; preds = %LeafBlock, %bb.1
ret void
}
PHINode should have one entry for each predecessor of its parent basic block!
%tmp = phi i3 [ 0, %LeafBlock ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ]
```
So it has removed the switch instruction but it only updated one of the five phi operands for %bb.0.
The input looked like
```
define void @v_257_0(i3 %0) {
bb.0:
switch i3 %0, label %bb.2 [
i3 -1, label %bb.1
i3 -2, label %bb.1
i3 2, label %bb.1
i3 1, label %bb.1
i3 0, label %bb.1
]
bb.1: ; preds = %bb.0, %bb.0, %bb.0, %bb.0, %bb.0
%tmp = phi i3 [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ], [ 0, %bb.0 ]
br label %bb.2
bb.2: ; preds = %bb.1, %bb.0
ret void
}
```
So there is one phi operand for each of the values that makes it jump from %bb.0 to %bb.1 and lower-switch only updated one of them when it changed things.
[bbi-95731.ll.gz](https://github.com/llvm/llvm-project/files/15414163/bbi-95731.ll.gz)
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